Filters in Twig can be used to modify variables. Filters are separated from the variable by a pipe symbol (|) and may have optional arguments in parentheses. Multiple filters can be chained. The output of one filter is applied to the next.

Example: {{ ponies|safe_join(", ")|lower}}

The list of filters that can be used in Twig templates for Drupal consists of all the filters in the Twig engine as well as some Drupal specific filters.